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Monday, 21 January 2008

With a deft mix of brain imaging and memory testing, researchers in Sweden believe they've identified neural activity that is responsible for controlling what information is allowed into our working memory - the mental store we use over brief periods, such as when dialling a phone number.

This activity, which was observed in the globuspallidus (part of a larger cluster of subcortical cells called the basal ganglia) acts as a kind of bouncer to working memory, keeping out the irrelevant riff raff.

Twenty-five female participants had their brains scanned while they memorised the location of squares and/or circles in a circular grid. An instruction before each trial informed them whether the circles, if present, were on the guest list - that is, whether they should be remembered or ignored.

Brain activity observed during these instructions increased in parts of the prefrontal cortex and the globuspallidus - reflecting the metaphorical bouncer readying himself for action.

The amount of filtering activity shown by the bouncer (in this case, in the globuspallidus, but not the prefrontal cortex) was related to how much memory-related activity was observed near the crown of the head, in the parietal cortex, when the participants were presented with a mix of squares to be remembered and circles to be ignored. That is, participants who showed less bouncer-type activity subsequently showed more memory-store activity when to-be-ignored circles were present. This makes perfect sense because it suggests more irrelevant material had been allowed into their working memory.

Of course, storing irrelevant material is inefficient and in a separate memory test, outside of the brain scanner, the participants with the more active 'memory bouncers' were found to have more working memory capacity.

"The present results therefore reveal a specific neural mechanism by which an individual's ability to exert control over the encoding of new information is linked to their working memory capacity," Fiona McNab and colleagues concluded.
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